I think it is much simpler than KCI or first touching by K. The applied force is the kick not the helmet. I would have nothing BUT touchback, R 1/10 @ R's 20...
Why reinvent the wheel.
NWA, you're right about the force and, within the strict limits of the OP, everything "works out".
With that said, for consideration, I would submit that there should always be a bean bag at the spot of first touching. Should the ball NOT end up going into R's EZ, but rather went OOB between the 5 and GL, we would have no "salable" first touching spot; nor would we have the PSK spot if R fouled during the kick.
Then, as pointed out earlier, if there is an R player in position to catch the kick, we would have KCI - which would be enforced from the spot of the touch.
So, I think it is always just good (and potentially safer) mechanics to bean bag spot of first touching).
We can never be sure where a football will bounce.....